In general, a so-called fiber or felt-tip pen or marker can be described as a writing instrument having a barrel which is provided at the writing end thereof with a writing tip from which a writing fluid, for convenience referred to as an ink, is transferred in a thin layer or film and in liquid form to the surface to which the transfer to the writing medium is to be made. Characteristic of such instruments is the fact that the tip draws the liquid ink from a reservoir in the barrel of the instrument by a wicking action, i.e. by capillarity so that the tip or "nib" can be termed a writing wick.
The writing wick or nib can be of various types and generally can be a sheathed wick or an unsheathed wick. A sheathed wick can be a comparatively thin nib encased in a metal sleeve while the unsheathed wick can have a relatively thick writing tip of the type commonly seen in so-called felt-tip markers.
The writing end of the tip can be round or of a different shape, the diameter can be rotationally symmetrically stepped or the felt wicking body can be stepped so that a thinner portion or a portion of reduced cross section reaches toward the ink reservoir.
Corresponding retaining systems must be provided depending upon the shape and nature of the nib or writing wick.
In the British Pat. No. 1,317,312, the writing tip is referred to as a nib core for a fiber-tipped writing instrument and the rotationally symmetrically stepped nib core at its narrower cross section is pressed into the tip of the barrel or housing so that the friction between the housing and the barrel holds the nib in place. The narrow portion extends into the reservoir to draw the ink or writing medium therefrom. The step of the nib facilitates seating of the nib against the tip of the housing and hence the axial positioning of the nib when the latter is passed into the housing.
One of the disadvantages of this system is that to avoid extension of the nib against the retaining friction force, the length of the bore in which the nib is frictionally retained must be comparatively great and where the housing is of a soft material, the pressure which is applied along this length of the bore wall must be considerable so that the excessive hugging action of the housing on the nib tends to restrict the flow of the writing medium to the tip of the nib.
In a German patent document (utility model) DE-GM No. 1.977,740 the fiber nib is disposed in the bore of a synthetic resin sleeve which, in turn, is set into the opening in the tip of the housing of the writing instrument. This sleeve defines within the bore longitudinally extending venting passages which interconnect the ink reservoir with the ambient atmosphere and thus permit free flow of the ink to the wick formed by the fiber nib.
The attachment of the fiber nib utilizes projections disposed between these passages in the sleeve and which are pressed inward upon insertion of the sleeve in the housing, to grip the fiber nib. This arrangement is of limited versatility because it can only be utilized for one type of fiber nib and is also expensive so that the resulting writing instrument may have a prohibitive cost. Furthermore, the nib, sleeve and passage assembly of this system may also be of excessive length for many purposes.